Rasengan

The Rasengan is an A-rank technique created by the Fourth Hokage, Minato Namikaze, by observing theTailed Beast Ball. Minato spent three years developing the Rasengan; his intention was to take the shape transformation of one's chakra to the "highest possible point" and combine it with his chakra's nature affinity, creating a technique that did not need the aid of time-consuming hand seals to control. Although Minato died before he could accomplish the latter feat, this was eventually accomplished by his son, Naruto Uzumaki. Even without nature transformation, the Rasengan is still a powerful, versatile, and difficult technique to learn and master.